LIGHT EMITTING DIODE

In our phones, our cars and even our homes. Any time something electronic lights up, there’s a good chance that an LED is behind it. They come in a huge variety of sizes, shapes, and colors, but no matter what they look like they have one thing in common: they’re the bacon of electronics. They’re widely purported to make any project better and they’re often added to unlikely things.
LEDs are a particular type of diode that convert electrical energy into light. In fact, LED stands for “Light Emitting Diode” .And this is reflected in the similarity between the diode and LED schematic symbols:
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A light-emitting diode (LED) is a two-leadsemiconductors light source. It is a p-n junction diode that emits light when activated. When a suitable voltage is applied to the leads, electrons are able to recombine with electron hole within the device, releasing energy in the form of photons.
A P-N junction can convert absorbed light energy into a proportional electric current. The same process is reversed here (i.e. the P-N junction emits light when electrical energy is applied to it). This phenomenon is generally called electroluminescence, which can be defined as the emission of light from a semiconductors under the influence of an electric field . The charge carriers recombine in a forward-biased P-N junction as the electrons cross from the N-region and recombine with the holes existing in the P-region. Free electrons are in the cconduction band of energy levels, while holes are in the valence energy band. Thus the energy level of the holes is less than the energy levels of the electrons. Some portion of the energy must be dissipated to recombine the electrons and the holes. This energy is emitted in the form of heat and light.
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The electrons dissipate energy in the form of heat for silicon and germanium diodes but in  gallium arsenide phosphide(GaAsP) and  gallium phosphide(GaP) semiconductors, the electrons dissipate energy by emitting photons. If the semiconductor is translucent, the junction becomes the source of light as it is emitted, thus becoming a light-emitting diode. However, when the junction is reverse biased, the LED produces no light and—if the potential is great enough, the device is damaged.


K.Aishwarya.Rao

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